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Old 29-11-2014, 09:15   #16
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Re: Lightening protection on a cat

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Mark, what's happening to the aluminum of your mast where the copper is attached to it? I seem to keep learning the hard way that any two metals of different properties at all will have some reaction when in physical contact in the presence of salt spray. Even two different aluminums in a storm window. Electrons seem to flow, and aluminum seems to suffer if there's no zinc to take the fall.
The copper mount is tinned, which helps some but probably not much. The interface edges are sealed, which helps keep water out. While it can get splashed with salt water underway, rain washes that off quickly. So far I see no galvanic corrosion.

Attached are two graphs from a paper in the IEEE journal showing statistics from 71 sailboats hit by lightning. "Protected" and "unprotected" refer to grounding here.

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Old 29-11-2014, 09:42   #17
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Re: Lightening protection on a cat

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Attached are two graphs from a paper in the IEEE journal showing statistics from 71 sailboats hit by lightning. "Protected" and "unprotected" refer to grounding here.
Yep. Very little difference between protected and not protected in salt water.

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Old 29-11-2014, 09:57   #18
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Re: Lightening protection on a cat

so that's how people are getting confused. Protected doesn't mean you can prevent a strike. Protected means you're managing your strike for minimal damage.
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Old 29-11-2014, 10:00   #19
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Re: Lightening protection on a cat

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so that's how people are getting confused. Protected doesn't mean you can prevent a strike. Protected means you're managing your strike for minimal damage.
For which these graphs shows "management" doesn't work.

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Old 29-11-2014, 10:16   #20
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Re: Lightening protection on a cat

The authors state that there was a significant difference, even in salt water, in hull damage for ungrounded boats. Note that "1" means holes in the hull and "4" was a large and extended blowout.

There is little difference in electronics damages, as everyone expects. Tiny electronics components are just too sensitive to EMP, small currents, etc. They did note that surge suppression measures went a long way toward eliminating electronics damage - to the point of almost being prevention devices. Any data center already understands this, though.

The requirements for "protected" in the survey was very broad - a small wire attached to a keel bolt was considered as having some "protection". Galvanic bonding measures actually fit this definition. There was no proper definition of "protected" used - just that "unprotected" had no grounding/galvanic system or other measures taken.

They also note that the ABYC lightning bonding standards are insufficient in sizing (#8 wire, 12" plate, etc), and that boats with larger than ABYC suffered less damage.

Nowhere is any evidence that lightning bonding a boat attracted lightning or increase the chances of being hit.

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Old 30-11-2014, 09:10   #21
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Re: Lightening protection on a cat

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The authors state that there was a significant difference, even in salt water, in hull damage for ungrounded boats. Note that "1" means holes in the hull and "4" was a large and extended blowout.
Mark
Yet their data does not seem to bear this out. 71 is a very small sampling and the differences between damaged and undamaged, even in fresh water, are small.

For example, the percentage of boats suffering more serious damage looks to be around 7.5% (5.3 boats) for the "protected" boats and 9% (6.3 boats) for the "unprotected" boats. These differences do not seem statistically significant, but maybe one needs to read the whole article to see how they've drawn their conclusions.

That said, when we head south again, I am considering rigging a system much like Mark has done, but this will be more to protect me while I am near the mast than to protect the boat. My electronics are on their own.
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Old 30-11-2014, 10:55   #22
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Re: Lightening protection on a cat

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That said, when we head south again, I am considering rigging a system much like Mark has done, but this will be more to protect me while I am near the mast than to protect the boat.
How so? If you don't think that a lightning bonding system has any chance of containing and directing a strike to ground through it, why would you think you would be personally safer with one?

Mark
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Old 30-11-2014, 20:47   #23
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Re: Lightening protection on a cat

Hello Cruisers, Helia 44 here,

Since this could save someones Life, I will put on what I have found in the Carib on my Mason 48 about 25 years ago... While I was not on a Cat, the Person that taught me this WAS on a Cat, and had been hit 17 times in ten years in the Caribbean.. (Which I thought was a record) Further enhancing his credibility with me, was his Business: Engineering of Lightening Arrestors on Skyscrapers.. OK?

I was Cruising the Carib, and based in Florida, and if it is not the lightening capital of the World, it certainly ranks up there in the Hurricane season.. Anyway, in my Engineering, I was trying direct the lightening strike OUTSIDE OF THE HULL connecting cables to the upper and lower shrouds on each side. He spotted them rolled up inside the stanchions, as I would only roll them down into the water in lightening storms. Anyway he spotted the and said I had the right idea, directing the strike OUTSIDE of the hull, as an arc to the bonding system or below the mast step could kill someone on the inside or blow a hole in the hull below the water line...

Anyway, my system worked, but here is how he taught me to improve it: Put chain inside of clear poly tubing... I put (from memory 5/16 chain, inside of about 1" clear vinyl tubing, that way no scratches and it still coiled up and unrolled. What he said was why the chain, was micro resistance that blew the links like a fuse. The galvanized links conducted the juice, but not the extreme amperage, and the links would blow like a Circuit Breaker and stop the Strike all in a millisecond... He claimed the tests worked well on his yacht.... In fairness, I left Florida and the Caribbean, sold my boat, and Migrated to Australia before it was put to the test. However, I trust his expertise and experience and Engineering, as he was the only Skyscraper Lightening Arrestor Engineer on a yacht I have ever heard of or met...

I hope this is a help and saves someone's Life.... Helia 44
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Old 30-11-2014, 21:14   #24
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Re: Lightening protection on a cat

Helia 44,

As I am actively researching lightning mitigation right now, this was interesting.

What size chain are you proposing?

I thought chain would be a relatively poor conductor given the actual metal to metal contact surface area of a chain, and that the charge is carried mostly on the outside surface, from what I have read.

And when the "fuse blows", where does all that charge and amperage go?
Wouldn't it just jump to earth wherever it can? And if that is the case, wouldn't that be more dangerous?
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Old 30-11-2014, 21:25   #25
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Re: Lightening protection on a cat

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Helia 44,

As I am actively researching lightning mitigation right now, this was interesting.

What size chain are you proposing?

I thought chain would be a relatively poor conductor given the actual metal to metal contact surface area of a chain, and that the charge is carried mostly on the outside surface, from what I have read.

And when the "fuse blows", where does all that charge and amperage go?
Wouldn't it just jump to earth wherever it can? And if that is the case, wouldn't that be more dangerous?
Hi ya Big Beakie,
Look, we had lengthy discussions on this, and it was very interesting as he was an Engineer that specialized in this, and was paid big money as a Consultant on skyscrapers... Further, his sideline was Arrestors for Yachts.... What he told me was that it actually STOPPED the strike in a millisecond, like blowing a fuse. It did not go anywhere it just stopped the strike.

From memory (like 25 years ago) I was using 5/16" galvanized chain in clear vinyl tubing. Now I did not get to test it, but he said he had for years and it worked really well. Rather than just conducting the strike, which can cause serious damage, he was talking about breaking the strike: Stopping it in an thousandth of a second... At the time the key was the micro-resistance between the lengths that would blow with the mega amperage of the strike... It made sense at the time, as he explained it..

Mind you, he thought possibly he was hit more often than most BECAUSE he had this grounding system, that he could not be sure but it was either bad luck or attracted the strikes... hmmmmm In any case, he and his yacht survived multiple strikes, I mean I think it was 17 in 10 years.

Hmmm, don't know, but his credentials and Business card were impressive..

Helia 44
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Old 30-11-2014, 21:32   #26
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Re: Lightening protection on a cat

So it breaks the chain? And that is what stops the flow of electricity?
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Old 30-11-2014, 22:04   #27
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Re: Lightening protection on a cat

It has been 25 years, but from memory, from his descriptions I think he said it blew the link apart with a loud crack like gunfire. I mean it BLEW the links apart, like blowing a massive fuse....

There was enough of a conductor to start the strike, but it could not carry the huge mega amperage, so it blows the links apart... According to him, he had seen it work many times, and at the time it was his current recommendation. I had a little boy, two year old at the time, cute little bugger (now 6'3") but anyway I think when he saw my rigging job coiled up and the little boy on deck, he took a liking and we had a few sessions as he would stop back by to see my progress as I switched over to his system.

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Old 30-11-2014, 22:09   #28
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Re: Lightening protection on a cat

Ok, cool. Thanks for that.

It's good to get ideas and have a think about a workable system.
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Old 01-12-2014, 07:31   #29
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Re: Lightening protection on a cat

Look, just think about this "stopping the strike" thing for a moment and you will realize it is silly.

If this was valid, then all anyone would need is a metal rod on the top of the mast with a fuseable link in it. Also, the fuses in electronics would be sufficient protection. Not to mention that no ungrounded boat would ever suffer hull damage because the lightning energy would simply "stop" before jumping 1-3' through the hull into the water.

Heck, even big lightning surge protectors that protect all communications centers, data centers, etc don't operate that way. They clamp the energy by shorting it to ground - not simply breaking the link.

None of what you think that guy told you makes any sense or is in line with any other studies or experiences.

Mark
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Old 01-12-2014, 07:41   #30
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Re: Lightening protection on a cat

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Originally Posted by colemj View Post
How so? If you don't think that a lightning bonding system has any chance of containing and directing a strike to ground through it, why would you think you would be personally safer with one?

Mark
I don't really. That's probably why I have not yet got around to doing it. I already have a long length of 4-0 cable (in yellow, so the lightning knows that it's a ground) and it would be a simple matter to bolt it to the mast and run it through a hole in the deck. My hope is that it might prevent a side flash while I am in the cockpit. I'm not at all confident that it would work, but if there is any chance that it would, why not give it a try? It's got to be better than what I am using now:
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